Base profile of self-aligned bipolar transistors for power amplifier applications

ABSTRACT

According to a bipolar transistor structure having a transistor top and a transistor bottom herein, a silicon substrate located at the transistor bottom has a collector region of a first conductivity type. An epitaxial base layer of a second conductivity type overlies, relative to the transistor top and bottom, a portion of the collector region. The epitaxial base layer has a bottom surface on the silicon substrate and a top surface opposite the bottom surface. A top region, relative to the transistor top and bottom, of the epitaxial base layer comprises a concentration of germanium having atomic compositions sufficient to avoid impacting transistor parameters, and sufficient to be resistant to selective chemical etching. A silicon emitter layer of the first conductivity type overlies, relative to the transistor top and bottom, a portion of the epitaxial base layer adjacent to the top surface of the epitaxial base layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.14/059,531, filed Oct. 22, 2013, the complete disclosure of which isincorporated herein by reference.

BACKGROUND

The present disclosure relates generally to integrated circuit devices,and more specifically, to a self-aligned bipolar transistor.

A bipolar junction transistor (BJT or bipolar transistor) is a type oftransistor that relies on the contact of two types of semiconductor forits operation. One type of semiconductor is formed with positive-typedopants, and is therefore referred to as a P-type semiconductor, whileanother type of semiconductor is formed with negative-type dopants, andis therefore referred to as an N-type semiconductor. A bipolar junctiontransistor usually includes two back-to-back p-n junctions that share athin common region. In other words, a bipolar junction transistortypically includes three regions, two outer regions commonly known as“emitter” and “collector” respectively, and a middle region commonlyknown as “base”. Electrical connections are generally made to all threeregions.

Bipolar junction transistors can be used as amplifiers, switches, or inoscillators. Bipolar junction transistors come in two types, orpolarities, known as PNP and NPN, with the P and the N representing thedifferent doping types of the three main terminal regions (collector,base, and emitter). An NPN transistor comprises two semiconductorjunctions that share a thin P-doped anode region, and a PNP transistorcomprises two semiconductor junctions that share a thin N-doped cathoderegion.

Improvement in transistor performance, especially its operation speed,is generally considered as essential for achieving improved performanceof an integrated circuit wherein various types of transistors arenormally used. Bipolar transistors with a silicon germanium (“SiGe”)intrinsic base may be capable of delivering performance required forsuch integrated circuit. To achieve higher electrical performance, thesetransistors typically have a doped polysilicon extrinsic base layer ontop of or adjacent to the epitaxially grown intrinsic SiGe base. So far,SiGe-HBTs have demonstrated cut-off frequency (f_(T)) of up to 400 GHz.The emitter to collector transit time of such a transistor is typicallyreduced by optimizing the Ge/Si ratio, doping profile, and filmthickness of the epitaxially grown intrinsic SiGe base. Such devices areused, for example, in integrated circuits fabricated for highperformance mixed signal applications.

SUMMARY

According to a bipolar transistor structure having a transistor top anda transistor bottom herein, a silicon substrate located at thetransistor bottom has a collector region of a first conductivity type.An epitaxial base layer of a second conductivity type overlies, relativeto the transistor top and the transistor bottom, a portion of thecollector region. The epitaxial base layer has a bottom surface on thesilicon substrate and a top surface opposite the bottom surface. A topregion, relative to the transistor top and the transistor bottom, of theepitaxial base layer comprises a concentration of germanium havingatomic compositions sufficient to avoid impacting transistor parameters,and sufficient to be resistant to selective chemical etching. A siliconemitter layer of the first conductivity type overlies, relative to thetransistor top and the transistor bottom, a portion of the epitaxialbase layer adjacent to the top surface of the epitaxial base layer.

According to a device having a device top and a device bottom herein, ann-type doped collector of a bipolar transistor is disposed in an upperportion, relative to the device top and the device bottom, of a silicon(Si) substrate layer. A base of p-type doped epitaxial silicon germanium(SiGe) is disposed on the substrate above, relative to the device topand the device bottom, the n-type doped collector. A top region of thebase, relative to the device top and the device bottom, comprises aconcentration of germanium (Ge) having atomic compositions sufficient toavoid impacting transistor parameters, and sufficient to be resistant toselective chemical etching. An n-type doped silicon (Si) emittercontacts the base.

According to a method of forming a bipolar transistor structure herein,a collector region of a first conductivity type is formed within asemiconductor substrate. A base of a second conductivity type is formedon a portion of the collector region. An etch-stop region is formed in asurface layer of the base. The surface layer is located opposite thesemiconductor substrate. A concentration of germanium in the etch-stopregion is controlled to have atomic compositions sufficient to avoidimpacting transistor parameters and sufficient to be resistant toselective chemical etching. An emitter of the first conductivity type isformed on the etch-stop region of the base.

BRIEF DESCRIPTION OF THE DRAWINGS

The devices and methods herein will be better understood from thefollowing detailed description with reference to the drawings, which arenot necessarily drawn to scale and in which:

FIG. 1 is an elevational view of a bipolar transistor structureaccording to devices and methods herein;

FIG. 2 is a graph showing the profiles of constituent in the baseportion according to devices and methods herein;

FIG. 3 is a schematic diagram of a partially completed integratedcircuit structure according to devices and methods herein;

FIG. 4 is a schematic diagram of an enlarged portion of the partiallycompleted integrated circuit structure according to devices and methodsherein;

FIG. 5 is a schematic diagram of a partially completed integratedcircuit structure according to devices and methods herein;

FIG. 6 is a schematic diagram of a partially completed integratedcircuit structure according to devices and methods herein;

FIG. 7 is a schematic diagram of a partially completed integratedcircuit structure according to devices and methods herein;

FIG. 8 is a schematic diagram of a partially completed integratedcircuit structure according to devices and methods herein;

FIG. 9 is a schematic diagram of a partially completed integratedcircuit structure according to devices and methods herein;

FIG. 10 is a schematic diagram of a partially completed integratedcircuit structure according to devices and methods herein;

FIG. 11 is a schematic diagram of a partially completed integratedcircuit structure according to devices and methods herein;

FIG. 12 is a schematic diagram of a partially completed integratedcircuit structure according to devices and methods herein;

FIG. 13 is a schematic diagram of a partially completed integratedcircuit structure according to devices and methods herein;

FIG. 14 is a flow diagram illustrating devices and methods herein; and

FIG. 15 is a schematic diagram of a hardware system according to devicesand methods herein.

DETAILED DESCRIPTION

It will be readily understood that the devices and methods of thepresent disclosure, as generally described and illustrated in thedrawings herein, may be arranged and designed in a wide variety ofdifferent configurations in addition to the devices and methodsdescribed herein. Thus, the following detailed description of thedevices and methods, as represented in the drawings, is not intended tolimit the scope defined by the appended claims, but is merelyrepresentative of selected devices and methods. The followingdescription is intended only by way of example, and simply illustratescertain concepts of the devices and methods, as disclosed and claimedherein.

Referring to the drawings, FIG. 1 shows a portion of a semiconductorwafer, indicated generally as 111. The wafer 111 comprises a multi-layersubstrate 114 forming a transistor 117. Generally, transistor structuresare formed by depositing or implanting impurities into a substrate toform at least one semiconductor channel region, bordered by shallowtrench isolation regions below the top (upper) surface of the substrate.A “substrate” herein can comprise any material appropriate for the givenpurpose (whether now known or developed in the future) and can comprise,for example, Si, SiC, SiGe, SiGeC, other III-V or II-VI compoundsemiconductors, or organic semiconductor structures, etc. The shallowtrench isolation structures are well-known to those ordinarily skilledin the art and are generally formed by patterning openings/trencheswithin the substrate and growing or filling the openings with a highlyinsulating material (this allows different active areas of the substrateto be electrically isolated from one another).

The transistor 117 includes a collector 120, a base 123 comprising anintrinsic base portion 126 and an extrinsic base portion 129, and aself-aligned emitter 132. The base 123 may be a thick layer providingmore mechanical strength and lower base resistance. Moreover, the flat,top portion enables better silicide formation, as described in moredetail below. Each of the collector 120, base 123, and emitter 132 isformed in one or more layers of the multi-layer substrate 114, asdescribed in further detail below. Typically, in bipolar complementarymetal oxide semiconductor (BiCMOS) transistors, the collector 120 is inthe substrate 114, where CMOS FETs are built first. The base 123 and theemitter 132 are created later. The base 123 is grown epitaxially.Typically, the emitter 132 is formed by deposition of poly silicon.According to devices and methods herein, the emitter layer is grownepitaxially, in order to make it substantially single crystalline.

FIG. 2 shows a specific structural profile for the base portion of thetransistor 117 in FIG. 1. In FIG. 2, the abscissa represents the depthfrom the upper surface of the layer forming the emitter 132 (labeled‘a’) to the bottom surface of the layer forming the collector 120(labeled ‘b’), and the ordinate represents the content or concentrationof germanium (Ge) (indicated by the solid line 135). Carbon and boron(not shown) may also be included during a certain stage of the epitaxialgrowth of the base layer, as is known to those skilled in the art.

According to the specific profile shown in FIG. 2, the germanium profileshows that the Ge content in the layer forming the base 123 is at aminimum (about 0%) at the interface between the base 123 and thecollector 120 as well as at some point between the top surface of thebase 123 and the emitter 132. The concentration of germanium increasesin the layer to a maximum (up to about 40%) between the top interfaceand the bottom interface. Additionally, the base 123 includes anetch-stop region 143 having a thin layer of germanium (up to about 15%)at the surface. Note: a triangular Ge profile (in cross-section) isshown, other profiles, such as a trapezoid shape (in cross-section) arealso applicable.

In the base profile, the components maintain mechanical strength of thestructure. According to devices and methods herein, the etch-stop region143 of the base 123 is built with a surface layer or layers such thatthe top surface layer or entire layers have Ge atomic compositions thatare low enough (e.g., <15%) not to impact the original deviceparameters, but high enough (e.g., >1%) to be resistant to selectivechemical etching. According to devices and methods herein, the etch-stoplayer may be formed in the base portion in one epitaxial growth step.

FIGS. 3-13 illustrate an integrated circuit structure (e.g., bipolarjunction transistor) in various processing stages. More specifically, asillustrated in FIG. 3, exemplary methods herein form an n-typedopant-implanted sub-collector region 303 within a substrate 306. Thesubstrate 306 may comprise any conventional semiconductor substrate suchas, for example, a bulk silicon substrate or an active layer ofsemiconductor material of a silicon-on-insulator (SOI) wafer. Themethods herein epitaxially grow a base layer 309 from the substrate 306.In one example, the epitaxial growth process can be a low temperatureepitaxial (LTE) growth process (typically at a growth temperatureranging from 400° C. to 850° C.). Epitaxial films may be grown fromgaseous or liquid precursors. Because the substrate 306 acts as a seedcrystal, the deposited film of the base layer 309 may lock into one ormore crystallographic orientations with respect to the crystalorientation of the substrate 306. The base layer 309 is epitaxiallygrown having a predetermined SiGe base profile, such as the oneillustrated in FIG. 2.

As noted above, bipolar junction transistors are generally either NPN orPNP semiconductor structures; therefore, the polarity of the dopant forthe collector region 303 will be opposite the polarity of the dopantused for the material of the base layer 309. For purposes herein, a“semiconductor” is a material or structure that may include an implantedimpurity or may be in-situ doped during the epitaxial growth, whichallows the material to sometimes be a conductor and sometimes be aninsulator, based on electron and hole carrier concentration. As usedherein, “implantation processes” can take any appropriate form (whethernow known or developed in the future) and can comprise, for example, ionimplantation, etc.

A positive-type transistor “P-type transistor” uses impurities such asboron, indium or gallium, etc., within an intrinsic semiconductorsubstrate (to create deficiencies of valence electrons) as asemiconductor region. Similarly, an “N-type transistor” is anegative-type transistor that uses impurities such as antimony, arsenicor phosphorous, etc., within an intrinsic semiconductor substrate (tocreate excessive valence electrons) as a semiconductor region.

Also for purposes herein, an “insulator” is a relative term that means amaterial or structure that allows substantially less (<95%) electricalcurrent to flow than does a “conductor.” The dielectrics (insulators)mentioned herein can, for example, be grown from either a dry oxygenambient or steam, and then patterned. Alternatively, the dielectricsherein may be formed from any of the many candidate high dielectricconstant (high-k) materials, including but not limited to siliconnitride, silicon oxynitride, a dielectric stack of SiO₂ and Si₃N₄, andmetal oxides like tantalum oxide. The thickness of dielectrics hereinmay vary contingent upon the required device performance.

FIG. 4 shows an enlarged view of the etch-stop region 143 of the base123 forming the etch-stop layer, according to devices and methodsherein. The etch-stop region 143 may comprise a silicon region 405sandwiched between the base layer 309 and a thin silicon germanium(SiGe) region 414. The thin SiGe region 414 may have Ge atomiccompositions that are sufficient, e.g., <15%, not to impact the originaldevice parameters, but sufficient, e.g., >1%, to be resistant toselective chemical etch. According to devices and methods herein, anadditional thin layer of Si 423 may be provided on the SiGe region 414on top of the profile.

As shown in FIG. 5, an in-situ doped (ISD) emitter layer 312 isdeposited on the base layer 309, above the etch-stop region 143.According to devices and methods herein, the emitter layer 312 may beheavily doped initially, and undoped at the surface layer 315. Theprocessing steps then form an insulating layer 318 (such as a depositedor oxidized material) on the top of the emitter layer 312. Manydifferent insulators could be utilized by various deposition techniques.

Referring to FIG. 6, narrow isolation trenches 606 are etched throughthe emitter layer 312 and base layer 309, and at least partially intothe substrate 306. Any suitable etch may be used to form the trenches606, such as a selective RIE process. In general, two trenches 606 maybe formed, one on the left and another one on the right. In onenon-limiting example, the trenches 606 may have a width “w” of about 0.2μm and a space between the two trenches “d” of about 1.2 μm. It iscontemplated that the present disclosure is not limited to theseexemplary dimensions, however, and any suitable width and diameter maybe used with the trench 606 as appropriate.

As shown in FIG. 7, undercuts are formed in the trenches 606. A topundercut 609 is formed in the emitter layer 312, and a bottom undercut612 is formed in a portion of the base layer 309 and a portion of thesubstrate 306. In one non-limiting example, the top undercut 609 may golaterally a distance “u” of about 0.4 μm leaving an emitter stack 615having a width “w” of about 0.4 μm. It is contemplated that the presentdisclosure is not limited to these exemplary dimensions, however, andany suitable size of the top and bottom undercuts 609, 612 may be used,as appropriate. Note: by undercutting, the sidewall of the emitter stack615 may not be entirely straight. The bottom undercut 612 may bewedge-shaped to form the intrinsic base portion 126 and the overhangingextrinsic base portion 129 of the transistor 117.

Referring to FIG. 8, a passivation liner 618 comprising an electricalinsulator material may be formed on the exposed surfaces of the topundercut 609 and bottom undercut 612, including the sidewalls andbottom. The passivation liner 618 may be formed by thermal oxidationand/or a thin layer of oxide deposition. It is contemplated that thepassivation liner 618 may be formed using conventional semiconductorprocesses and any suitable insulator material. For example, thepassivation liner 618 may be formed using a conformal depositionprocess, such as chemical vapor deposition (CVD). In some non-limitingexamples, the passivation liner 618 may be composed of the same materialas the insulating layer 318, e.g., silicon dioxide. According to devicesand methods herein, the passivation liner 618 may be thinly formed. Forexample, the passivation liner 618 may have a thickness of only about 5Å, although other thicknesses may be used.

Following sidewall passivation, nitride sidewall spacers 621 may beformed on the passivation liner 618, as shown in FIG. 9. According todevices and methods herein, the processing steps deposit a nitride layerand etch the nitride to form the sidewall spacers 621. For purposesherein, “sidewall spacers” are structures that are well-known to thoseordinarily skilled in the art and are generally formed by depositing orgrowing a conformal insulating layer (such as any of the insulatorsmentioned above) and then performing a directional etching process(anisotropic) that etches material from horizontal surfaces at a greaterrate than it removes material from vertical surfaces, thereby leavinginsulating material along the vertical sidewalls of structures. Thismaterial left on the vertical sidewalls is referred to as sidewallspacers.

When patterning any material herein, the material to be patterned can begrown or deposited in any known manner and a patterning layer (such asan organic photoresist) can be formed over the material. The patterninglayer (resist) can be exposed to some pattern of light radiation (e.g.,patterned exposure, laser exposure, etc.) provided in a light exposurepattern, and then the resist is developed using a chemical agent. Thisprocess changes the physical characteristics of the portion of theresist that was exposed to the light. Then one portion of the resist canbe rinsed off, leaving the other portion of the resist to protect thematerial to be patterned (which portion of the resist that is rinsed offdepends upon whether the resist is a positive resist (illuminatedportions remain) or negative resist (illuminated portions are rinsedoff). A material removal process is then performed (e.g., plasmaetching, etc.) to remove the unprotected portions of the material belowthe resist to be patterned. The resist is subsequently removed to leavethe underlying material patterned according to the light exposurepattern (or a negative image thereof).

In FIG. 10, a photo resist mask 625 may be applied to protect thecontact regions for the base 123 and emitter 132. Non-selective RIE canbe used to open contact regions for the collector 120, as shown in FIG.11.

As depicted in FIG. 12, portions of the dielectric layer are removed,and conventional processes may then be carried out to complete formationof the transistor 117, including forming self aligned silicide pads 631,632 on the base 123, silicide pad 634 on the emitter 132, and silicidepads 636, 637, 638, 639 for the collector 120. For example, TiSi₂,CoSi₂, or NiSi silicides may be formed by conventional processesincluding titanium or cobalt deposition followed by silicide formationand annealing processes to achieve the low electrical resistancesilicide phase, as is known in the art.

As depicted in FIG. 13, the trenches may be filled by a barrier nitridelayer and a dielectric material 642 comprising any suitable insulator,such as silicon dioxide (SiO₂), borophosphosilicate glass (BPSG), etc.Contacts may be formed in the dielectric material 642 to provideelectrical connections to the transistor 117. For example, an emittercontact 644 may be formed to connect to the silicide pad 634 on theemitter 132. One or more base contacts, such as 647, 648 may be formedto connect to the silicide pads 631, 632 on the base 123. One or morecollector contacts, such as 671, 672 may be formed to connect to thesilicide pads 636, 639 for the collector 120. Collector contacts canalso be made to the silicide pads 637, 638 at the bottom of thetrenches. The contacts may be formed in any desired manner, such asmasking the dielectric material 642, etching trenches in the dielectricmaterial 642, and filling the trenches with an electrically conductivematerial (e.g., tungsten, etc.), followed by chemical-mechanicalpolishing (CMP) of conductive material outside the trenches.Multiple-levels of metal wiring may be used to link transistors in apre-determined way, as is well known in the art.

Thus, as shown, such methods produce various integrated circuitstructures (such as PNP or NPN bipolar junction transistors). Suchintegrated circuit structures include a collector region 680 within asubstrate 306. An epitaxial base material is positioned on the collectorregion 680. The epitaxial base material has a SiGe base profile, e.g. asillustrated in FIG. 2. This epitaxial base material comprises a baseregion 683 on the collector region 680. Further, an emitter 132 ispositioned on the base region 683. The emitter 132 comprises a firstregion 686, contacting the base region 683, comprising silicon and asecond region 689, remote from the base region 683, comprising aconcentration of germanium.

FIG. 14 is a flow diagram illustrating the processing flow of anexemplary method of fabricating a bipolar transistor structure accordingto devices and methods herein. At 712, a collector region of a firstconductivity type is formed in a semiconductor substrate. A base of asecond conductivity type is epitaxially formed above a portion of thecollector region, at 724. A concentration of germanium in the base iscontrolled initially from a minimum amount. The concentration ofgermanium in the base is gradually increased to a maximum amount. Thenthe concentration of germanium in the base is gradually decreased to theminimum amount. At 736, an etch-stop region is formed in a top portionof the base. The etch-stop region may have Ge atomic compositions thatare sufficient, e.g., <15%, not to impact the original deviceparameters, but sufficient, e.g., >1%, to be resistant to selectivechemical etch. An emitter of the first conductivity type is formed abovea portion of the base, at 748.

The methods described herein can be used in fabricating a SiliconGermanium (SiGe) bipolar device or any complementary metal oxidesemiconductor (CMOS) device.

The method as described above may be used in the fabrication ofintegrated circuit chips. The resulting integrated circuit chips can bedistributed by the fabricator in raw wafer form (that is, as a singlewafer that has multiple unpackaged chips), as a bare die, or in apackaged form. In the latter case, the chip is mounted in a single chippackage (such as a plastic carrier, with leads that are affixed to amotherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case, the chip isthen integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a motherboard, or (b) an end product. The end productcan be any product that includes integrated circuit chips, ranging fromtoys and other low-end applications to advanced computer products havinga display, a keyboard or other input device, and a central processor.

For electronic applications, semiconducting substrates, such as siliconwafers, can be used. The substrate enables easy handling of the microdevice through the many fabrication steps. Often, many individualdevices are made together on one substrate and then singulated intoseparated devices toward the end of fabrication. In order to fabricate amicrodevice, many processes are performed, one after the other, manytimes repeatedly. These processes typically include depositing a film,patterning the film with the desired micro features, and removing (oretching) portions of the film. For example, in memory chip fabrication,there may be several lithography steps, oxidation steps, etching steps,doping steps, and many others are performed. The complexity ofmicrofabrication processes can be described by their mask count.

A device according to devices and methods herein may include a siliconsubstrate having a collector region of a first conductivity type. Anepitaxial base layer of a second conductivity type overlies a portion ofthe collector region. The epitaxial base layer has a bottom surface onthe silicon substrate and a top surface. A concentration of germanium isat a minimum adjacent to the top surface and the bottom surface and theconcentration of germanium increases to a maximum between the topsurface and the bottom surface. A silicon emitter layer of the firstconductivity type overlies a portion of the epitaxial base layeradjacent to the top surface of the epitaxial base layer. The siliconemitter layer comprises a first region, contacting the epitaxial baselayer, comprising silicon and a second region, remote from the epitaxialbase layer, comprising a concentration of germanium.

While only one or a limited number of transistors are illustrated in thedrawings, those ordinarily skilled in the art would understand that manydifferent types of transistors could be simultaneously formed with thedevices herein and the drawings are intended to show simultaneousformation of multiple different types of transistors; however, thedrawings have been simplified to only show a limited number oftransistors for clarity and to allow the reader to more easily recognizethe different features illustrated. This is not intended to limit thisdisclosure because, as would be understood by those ordinarily skilledin the art, this disclosure is applicable to structures that includemany of each type of transistor shown in the drawings.

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatus(systems), and computer program products according to various devicesand methods. It will be understood that each block of the flowchartillustrations and/or two-dimensional block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. The computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

According to a further devices and methods herein, an article ofmanufacture is provided that includes a tangible computer readablemedium having computer readable instructions embodied therein forperforming the steps of the computer implemented methods, including, butnot limited to, the method illustrated in FIG. 14. Any combination ofone or more computer readable non-transitory medium(s) may be utilized.The computer readable medium may be a computer readable signal medium ora computer readable storage medium. The non-transitory computer storagemedium stores instructions, and a processor executes the instructions toperform the methods described herein. A computer readable storage mediummay be, for example, but not limited to, an electronic, magnetic,optical, electromagnetic, infrared, or semiconductor system, apparatus,or device, or any suitable combination of the foregoing. Any of thesedevices may have computer readable instructions for carrying out thesteps of the methods described above with reference to FIG. 14.

The computer program instructions may be stored in a computer readablemedium that can direct a computer, other programmable data processingapparatus, or other devices to function in a particular manner, suchthat the instructions stored in the computer readable medium produce anarticle of manufacture including instructions which implement thefunction/act specified in the flowchart and/or block diagram block orblocks.

Furthermore, the computer program instructions may also be loaded onto acomputer, other programmable data processing apparatus, or other devicesto cause a series of operational steps to be performed on the computer,other programmable apparatus or other devices to produce a computerimplemented process such that the instructions which execute on thecomputer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

In case of implementing the devices and methods herein by softwareand/or firmware, a program constituting the software may be installedinto a computer with dedicated hardware, from a storage medium or anetwork, and the computer is capable of performing various functions ifwith various programs installed therein.

A representative hardware environment for practicing the devices andmethods herein is depicted in FIG. 15. This schematic drawingillustrates a hardware configuration of an information handling/computersystem in accordance with the devices and methods herein. The systemcomprises at least one processor or central processing unit (CPU) 810.The CPUs 810 are interconnected via system bus 812 to various devicessuch as a Random Access Memory (RAM) 814, Read-Only Memory (ROM) 816,and an Input/Output (I/O) adapter 818. The I/O adapter 818 can connectto peripheral devices, such as disk units 811 and tape drives 813, orother program storage devices that are readable by the system. Thesystem can read the inventive instructions on the program storagedevices and follow these instructions to execute the methodology of thedevices and methods herein.

In FIG. 15, CPUs 810 perform various processing based on a programstored in a Read Only Memory (ROM) 816 or a program loaded from aperipheral device, such as disk units 811 and tape drives 813 to aRandom Access Memory (RAM) 814. In the RAM 814, required data when theCPUs 810 perform the various processing or the like is also stored, asnecessary. The CPUs 810, the ROM 816, and the RAM 814 are connected toone another via a bus 812. An I/O adapter 818 is also connected to thebus 812 to provide an input/output interface, as necessary. A removablemedium, such as a magnetic disk, an optical disk, a magneto-opticaldisk, a semiconductor memory, or the like, is installed on theperipheral device, as necessary, so that a computer program readtherefrom may be installed into the RAM 814, as necessary.

The system further includes a user interface adapter 819 that connects akeyboard 815, mouse 817, speaker 824, microphone 822, and/or other userinterface devices such as a touch screen device (not shown) to the bus812 to gather user input. Additionally, a communication adapter 820including a network interface card such as a LAN card, a modem, or thelike connects the bus 812 to a data processing network 825. Thecommunication adapter 820 performs communication processing via anetwork such as the Internet. A display adapter 821 connects the bus 812to a display device 823, which may be embodied as an output device suchas a monitor (such as a Cathode Ray Tube (CRT), a Liquid Crystal Display(LCD), or the like), printer, or transmitter, for example.

In the case where the above-described series of processing isimplemented with software, the program that constitutes the software maybe installed from a network such as the Internet or a storage mediumsuch as the removable medium.

Those skilled in the art would appreciate that the storage medium is notlimited to the peripheral device having the program stored therein asillustrated in FIG. 15, which is distributed separately from the devicefor providing the program to the user. Examples of a removable mediuminclude a magnetic disk (including a floppy disk), an optical disk(including a Compact Disk-Read Only Memory (CD-ROM) and a DigitalVersatile Disk (DVD)), a magneto-optical disk (including a Mini-Disk(MD) (registered trademark)), and a semiconductor memory. Alternatively,the storage medium may be the ROM 816, a hard disk contained in thestorage section of the disk units 811, or the like, which has theprogram stored therein and is distributed to the user together with thedevice that contains them.

As will be appreciated by one skilled in the art, aspects of the devicesand methods herein may be embodied as a system, method, or computerprogram product. Accordingly, aspects of the present disclosure may takethe form of an entirely hardware system, an entirely software system(including firmware, resident software, micro-code, etc.) or an systemcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module”, or “system.” Furthermore,aspects of the present disclosure may take the form of a computerprogram product embodied in one or more computer readable medium(s)having computer readable program code embodied thereon.

Any combination of one or more computer readable non-transitorymedium(s) may be utilized. The computer readable medium may be acomputer readable signal medium or a computer readable storage medium.The non-transitory computer storage medium stores instructions, and aprocessor executes the instructions to perform the methods describedherein. A computer readable storage medium may be, for example, but notlimited to, an electronic, magnetic, optical, electromagnetic, infrared,or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. More specific examples (a non-exhaustivelist) of the computer readable storage medium include the following: anelectrical connection having one or more wires, a portable computerdiskette, a hard disk, a random access memory (RAM), a Read-Only Memory(ROM), an Erasable Programmable Read-Only Memory (EPROM or Flashmemory), an optical fiber, a magnetic storage device, a portable compactdisc Read-Only Memory (CD-ROM), an optical storage device, a“plug-and-play” memory device, like a USB flash drive, or any suitablecombination of the foregoing. In the context of this document, acomputer readable storage medium may be any tangible medium that cancontain, or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including, but not limited to, wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++, or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer, or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousdevices and methods herein. In this regard, each block in the flowchartor block diagrams may represent a module, segment, or portion of code,which comprises one or more executable instructions for implementing thespecified logical function(s). It should also be noted that, in somealternative implementations, the functions noted in the block mightoccur out of the order noted in the Figures. For example, two blocksshown in succession may, in fact, be executed substantiallyconcurrently, or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved. It will also be notedthat each block of the block diagrams and/or flowchart illustration, andcombinations of blocks in the block diagrams and/or flowchartillustration, can be implemented by special purpose hardware-basedsystems that perform the specified functions or acts, or combinations ofspecial purpose hardware and computer instructions.

The terminology used herein is for the purpose of describing particulardevices and methods only and is not intended to be limiting of thisdisclosure. As used herein, the singular forms “a”, “an”, and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

In addition, terms such as “right”, “left”, “vertical”, “horizontal”,“top”, “bottom”, “upper”, “lower”, “under”, “below”, “underlying”,“over”, “overlying”, “parallel”, “perpendicular”, etc., used herein areunderstood to be relative locations as they are oriented and illustratedin the drawings (unless otherwise indicated). Terms such as “touching”,“on”, “in direct contact”, “abutting”, “directly adjacent to”, etc.,mean that at least one element physically contacts another element(without other elements separating the described elements).

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescriptions of the various devices and methods herein have beenpresented for purposes of illustration, but are not intended to beexhaustive or limited to the devices and methods disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describeddevices and methods. The terminology used herein was chosen to bestexplain the principles of the devices and methods, the practicalapplication or technical improvement over technologies found in themarketplace, or to enable others of ordinary skill in the art tounderstand the devices and methods disclosed herein.

What is claimed is:
 1. A method of forming a bipolar transistorstructure comprising: forming a collector region of a first conductivitytype within a semiconductor substrate; forming a base of a secondconductivity type on a portion of said collector region; forming anetch-stop region in a surface layer of said base, said surface layerbeing located opposite said semiconductor substrate; controlling aconcentration of germanium in said etch-stop region to have atomiccompositions between 1% and 15% at the top of said surface layer, saidconcentration of germanium being sufficient to avoid impactingtransistor parameters and sufficient to be resistant to selectivechemical etching; and forming an emitter of said first conductivity typeon said etch-stop region of said base.
 2. The method according to claim1, said forming said base comprising: epitaxially growing said basedirectly on said collector region.
 3. The method according to claim 1,said forming said emitter comprising: epitaxially growing said emitterdirectly on said base.
 4. The method according to claim 1, furthercomprising: forming a trench surrounding said collector regionsimultaneously with forming said emitter; and depositing an insulatorwithin said trench.
 5. The method according to claim 1, furthercomprising: forming sidewall spacers on sidewalls of said emitter. 6.The method according to claim 1, said base comprising an intrinsic baseportion and an extrinsic base portion, said method further comprising:forming silicide pads on said emitter, said collector region, and saidextrinsic base portion, and forming electrical contacts connected tosaid silicide pads.
 7. The method according to claim 1, saidconcentration of germanium in said base varying according to apredetermined profile, said predetermined profile being, incross-section, one of: triangular shaped; and trapezoidal shaped.
 8. Themethod according to claim 1, further comprising: forming a silicon layeroverlying said base.
 9. A method comprising: fabricating a device havinga device top and a device bottom, said device comprising: a collector ofa bipolar transistor comprising an n-type doped collector disposed in anupper portion, relative to said device top and said device bottom, of asilicon (Si) substrate layer; a base comprising p-type doped epitaxialsilicon germanium (SiGe) disposed on said Si substrate layer above,relative to said device top and said device bottom, said n-type dopedcollector, said base contacting said Si substrate layer, a top region ofsaid base, relative to said device top and said device bottom,comprising a concentration of germanium (Ge) having atomic compositionsbetween 1% and 15% at a top surface of said base, said concentration ofgermanium being sufficient to avoid impacting transistor parameters, andsufficient to be resistant to selective chemical etching; and an emittercomprising an n-type doped silicon (Si) emitter contacting said base.10. The method according to claim 9, further comprising: creating atrench surrounding said collector; and depositing an insulator withinsaid trench.
 11. The method according to claim 9, said base comprisingan intrinsic base portion and an extrinsic base portion, said methodfurther comprising: forming silicide pads and electrical contactsconnected to said emitter, said collector, and said extrinsic baseportion.
 12. The method according to claim 9, said base furthercomprising: a silicon layer overlying, relative to said device top andsaid device bottom, said top region of said base.
 13. The methodaccording to claim 9, said concentration of germanium in said basevarying according to a predetermined profile between said device top andsaid device bottom, said predetermined profile being, in cross-sectionbetween said device top and said device bottom, one of: triangularshaped; and trapezoidal shaped.
 14. A method comprising: providing asemiconductor substrate; forming a collector region of a firstconductivity type within said semiconductor substrate; forming a base ofa second conductivity type contacting a portion of said collectorregion; forming an etch-stop region in a surface layer of said base,said surface layer being located opposite said semiconductor substrate;controlling a concentration of germanium in said etch-stop region tohave atomic compositions between 1% and 15% at said surface layer, saidconcentration of germanium being sufficient to avoid impactingtransistor parameters and sufficient to be resistant to selectivechemical etching; and forming an emitter of said first conductivity typecontacting said etch-stop region of said base.
 15. The method accordingto claim 14, said forming said base further comprising: growing a singlecrystal epitaxially, directly on said collector region.
 16. The methodaccording to claim 14, said forming said emitter further comprising:growing a single crystal epitaxially, directly on said base.
 17. Themethod according to claim 14, further comprising: creating a trenchsurrounding said collector; and depositing an insulator within saidtrench.
 18. The method according to claim 14, said base comprising anintrinsic base portion and an extrinsic base portion, said methodfurther comprising: forming silicide pads attached to each of saidemitter, said collector, and said extrinsic base portion; and formingelectrical contacts connected to each of said silicide pads.
 19. Themethod according to claim 14, said concentration of germanium in saidbase varying according to a predetermined profile, said predeterminedprofile being, in cross-section, one of: triangular shaped; andtrapezoidal shaped.
 20. The method according to claim 14, furthercomprising: forming a silicon layer overlying said etch-stop region.